The most common cause of excessive back pressure is due to the accumulation of particulates and permanently adsorbed materials at the top of the HPLC Column. This could be precipitate or un-dissolved particles which can come from your samples or your mobile phase. The best way to minimize accumulation on your column is to filter your samples, solvents and buffers with a .45µm or a 0.2µm syringe filter or through a filter flask before use. This should give you more column lifetime. Another way to minimize this build up is to use either an inline solvent/mobile phase filters a guard column or a MicroSolv Column Saver. These disposable devices are low cost and easy to use without disrupting your chromatographic results.